2005 CR125 jetting

Discussion in 'Bike Mods, Performance, Maintenance & Repair' started by Joe_148, Jul 1, 2005.



  1. Joe_148

    Joe_148 Rookie DRN Member

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    Hey, hows it going.. Im having trouble jetting my new CR125 (2005). I got it about two months ago and have been trying to get it dialed in since then. My main problem is that Im still fouling plugs. The bike came with a 430 main (I put in a 420, but I have put the 430 back in because the plug was white when I was riding harder). The needle was on the 3rd clip, I put it on the second notch. It had a 55 pilot in it, I first went to a 50, then a 45. This is what im running right now, I thought I had it dialed in, but the other day I went trail riding and was going a bit slower and goofing around and I fouled plugs. Whenever I race, sitting on the line warming up I usually foul, or at least load up 2 times to the point where I just manage to save it from fouling. I beleive the air screw is at about 2 turns out. When I made the switch from the 50 to the 45, I noticed a significant difference in the power and sound of the bike. Now, I ordered a number 40 pilot, but Im not too sure on putting it in. The honda manual has a jetting guide for different altitudes and temperatures, and throughout every altitude even in the hottest of temperatures the leanest pilot they show (recommended) is a number 50. Just the thought of going down 3 sizes! from stock seems a bit crazy to me, and I cant beleive the other settings were pretty much spot on but the pilot is this out of whack? I think it has to be the pilot causing me to foul plugs, because its only when putting around or warming the bike up on the line. Other than fouling plugs (only when Im at low throttle openings) the bike runs great, the plug looks great when Im riding hard and I think all the other circuits are spot on. What do you think? Should I try out the number 40 pilot? If it matters, im running amsoil at 32:1 with premium gas (91 octane). It just makes me mad because previously I had a 2001 CR125 and I could play around and goof off on that thing forever, and I never once fouled a plug. With the new bike im always scared of it fouling so I cant just clown around with my friends I always have to be on it. Thanks alot for taking the time to read this, any reply is much appreciated.

  2. marcusgunby

    marcusgunby Lifetime Sponsor

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    You need to really lean the pilot as they are stupid rich-i think the 40 might work well.
  3. steve125

    steve125 Lifetime Sponsor

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    Lean the pilot jet until your air screw setting is in the 1.5-2.0 out range. A to lean pilot wont hurt the engine, may make it bog but thats it. Once you have the pilot lean enough, you may have to go back an re-set your needle clip position.

    When ever I change the needle clip position it also effects the jetting close to the pilot range, 1/8 to 1/4 throttle.

    If the pilot setting is perfect and I change the needle clip position 1 richer, then I usually turn the air screw 1/2 turn leaner(out). Same goes for the needle clip if I go richer, the air screw 1/2 turn leaner. This change(clip position/mixture) is due not to the needles taper but the needles "straight' section that overlaps in the pilots mixture range, and has now been re-positioned(leaner or richer) in the needle jet. Of course the clip position has a larger mixture effect on the 1/4 to 1/2 throttle range. Heres where the needles taper comes into play.

    So what alot of riders don't know is that when they change the clip position, they are changing 2 mixture settings, not just the one above the pilot mixture range.
  4. 05cr125ring-ding

    05cr125ring-ding Rookie DRN Member

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    I just called FMF trying to figure out the jetting for my 05 cr125. And what you need to do is put a 410 main jet a 50 pilot jet put the needle on the second clip and turn the air/fuel mixture 1.5 turns in. and it should run mint.
  5. IndyMX

    IndyMX Subscriber

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    2 1/2 year old post. Probably solved it by now.
  6. 05cr125ring-ding

    05cr125ring-ding Rookie DRN Member

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    I found it google trying to solve the problem my self and than solved it and I'm new to the site and didnt realize it was 2 years old until after i posted it
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